What Happens if I Charge MY Batteries Too Hard?

[walt]

Just out of curiosity (helps to be retired and have time to do completely unimportant stuff that takes a little time)..

I wondered about what the temperature rise of a battery maybe in the range of 200 plus or minus amp hour capacity would be if 50 amps were put into the battery for one hour.

Some assumptions that wont be reality but this is what they are. 50 amps is constant for the whole hour. Lead acid batteries are around about 85 percent efficient in charging so 7.5 amps go in heating the battery and 42.5 amps go into electrical energy. Assume the whole battery has the heat capacity of 150 pounds (or 68 Kg) of lead. So the power that goes into heating the battery at 13.3 volts would be 7.5 amps * 13.3 volts - 100 watts.

100 watts for one hour is 100 watt hours. Convert this KJ and this would be 361 KJ (note, google will do this conversion for you if you want to check).

Use the equation in this link https://www.engineeringtoolbox.com/specific-heat-metals-d_152.html and also use 0.13 as the specific heat for lead.

The equation is Q = Cp* Mass * T (check the units). Plugging all the above into this equation is

361 KJ - (.13 Kj/KgC) * (68 Kg) * (T in C)

T - 40.83 C

I have checked this a couple times as it seems way too high but this says that if you charge a lead acid battery that has about 150 pounds of lead in it for one hour at 50 amps, and you did not lose any heat to cooling while your were charging, the battery temperature would rise a really astounding 40.83 degrees C.

This of course makes a bunch of assumption that wont happen (like being able to charge for one hour at 50 amps) but this is still only putting 43.5 amp hours of electrical energy back into the battery.

So.. not exactly a real world example but I would consider battery heating if you did charge at a high current rate for a long time.

 

[jviss]

So.. not exactly a real world example but I would consider battery heating if you did charge at a high current rate for a long time.

You are on the right track, I think, but you could improve your analysis greatly if you added a term for cooling, i.e., determine the Θca, thermal resistance, case to ambient, which will shunt some of that heat.

 

[jviss]

I spoke with a technical support person at Trojan. He first quoted the 13% C(20) limit, and when I told him I had a limited charging time situation, he said I could go to 20%, but no more than 20%. He said "once you increase the rate you get more gassing, higher temperatures; the more rapid gassing you'll start eroding the plates - cause some of the active material to come off the plates - shorten performance, shorten life - increase temperature."

I then asked about temperature, and he said it should be kept below 120° F.

We chatted a while and he finished with "there's no fast charging when it comes to charging deep cycle batteries - there's just too much plate material."

So, I can hold my two battery, 230AH bank to 46A max during bulk - and I can do that at close to idle speeds on my engine. Or, if I charge harder, shorten the life and diminish the performance of my batteries.

My boat, my choice, right @Stu Jackson ?

 

[Stu Jackson]

Thanks for the report, much appreciated.

That said, what is the acceptance of your small house bank of, IIRC, 230 ah?

A nominal 400 ah house bank at 50% SOC can accept around 50A - after an initial but short-lived higher surge. We would expect that this smaller bank would accept less. So even with a large charge source like your 100A alternator with serpentine belt, it would be interesting to see if that's what it would produce via your Link 2000 R. Have you done that test?

 

[jviss]

That said, what is the acceptance of your small house bank of, IIRC, 230 ah?

A nominal 400 ah house bank at 50% SOC can accept around 50A - after an initial but short-lived higher surge. We would expect that this smaller bank would accept less. So even with a large charge source like your 100A alternator with serpentine belt, it would be interesting to see if that's what it would produce via your Link 2000 R. Have you done that test?

Stu, I'm honestly not trying to be obtuse, but I don't understand your use of term "acceptance" in this context.

When in bulk charging mode, while the battery voltage remains below the absorption voltage set-point, the alternator and regulator are acting as a constant current source, i.e., are current-regulated, and will (should) maintain that current throughout bulk; you set that current, and it is only limited by your alt-reg system and engine speed. By that I mean that it is possible for the alt-reg system to get out of regulation because if it's not able to produce the energy needed to maintain the current at the battery voltage.

On mine, with my 230AH bank, I can push 100A as long as I keep the engine speed up.

This is the charging current at about 1/2 way through bulk, maintained by keeping revs up.

But let's say, for argument's sake that you had an ideal current source, and you turned it up to an arbitrarily high current value; this current would indeed flow into the battery, and charge it, and perhaps, if it's too high, heat the battery, boil the electrolyte, erode the plates, and maybe even cause the battery to explode. As it heats, as a matter of fact, the internal resistance decreases, making things worse.

So, I don't know what my batteries' 'acceptance' is, during bulk, or what that means.

Once I reach the absorption voltage set-point - a voltage I choose (programmed), which in this case is the 14.8V (at 25° C) recommended by Trojan - the current will be determined by the batteries, since the charging source is now voltage regulated. And, as you know, it starts at some value and tapers off, approaching zero nearly asymptotically. At 2% C(20) it's generally considered fully charged.

Absorption is typically reached when the battery bank is up to 80% SOC, I think. I confess I haven't noticed or recorded at exactly what current it switches to at the onset of the absorption phase, but I think it's around 38A.

I have a recollection of at one time believing that a bank's 'acceptance' determined the bulk charging current, but I don't believe that any more. Maybe I lost some knowledge since I was obsessed with this topic 15 or so years ago, I don't know.

I'm sure had I a 460AH bank, i.e., double what I currently have, of the same kind of batts, I could pump 100A starting from 50% SOC all the way to 14.8V. And, it would be pretty close to acceptable according to Trojan's recommended 92A max.

 

[Davidasailor26]

Stu, I'm honestly not trying to be obtuse, but I don't understand your use of term "acceptance" in this context.

When in bulk charging mode, while the battery voltage remains below the absorption voltage set-point, the alternator and regulator are acting as a constant current source, i.e., are current-regulated, and will (should) maintain that current throughout bulk; you set that current, and it is only limited by your alt-reg system and engine speed. By that I mean that it is possible for the alt-reg system to get out of regulation because if it's not able to produce the energy needed to maintain the current at the battery voltage.

On mine, with my 230AH bank, I can push 100A as long as I keep the engine speed up.

This is the charging current at about 1/2 way through bulk, maintained by keeping revs up.

But let's say, for argument's sake that you had an ideal current source, and you turned it up to an arbitrarily high current value; this current would indeed flow into the battery, and charge it, and perhaps, if it's too high, heat the battery, boil the electrolyte, erode the plates, and maybe even cause the battery to explode. As it heats, as a matter of fact, the internal resistance decreases, making things worse.

So, I don't know what my batteries' 'acceptance' is, during bulk, or what that means.

Once I reach the absorption voltage set-point - a voltage I choose (programmed), which in this case is the 14.8V (at 25° C) recommended by Trojan - the current will be determined by the batteries, since the charging source is now voltage regulated. And, as you know, it starts at some value and tapers off, approaching zero nearly asymptotically. At 2% C(20) it's generally considered fully charged.

I agree with Jviss's explanation, and it's also consistent with, for example, this picture from https://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

You can think of the battery as a variable resistor, with increasing resistance as its SOC increases. Also think of V=IR. At low SOC, R is low, so V stays low, limited by the fact that I can only be so high (100A in jviss's case). As SOC increases, R increases, until eventually V can reach your set absorption voltage (14.8). Then, as R increases, and V is held at 14.8, I must decrease.

Absorption is typically reached when the battery bank is up to 80% SOC, I think. I confess I haven't noticed or recorded at exactly what current it switches to at the onset of the absorption phase, but I think it's around 38A.

Absorption starts when you leave bulk, which is where you reach your voltage set point. At that transition current should just start to drop from your maximum output. The BatteryUniversity link above seems to say the bulk/absorption transition happens around 70% SOC, but I'd imagine that depends on the size of your current source (with a larger source transitioning earlier).

 

[jviss]

Thanks David. I'm sure Stu knows all of that, too, what we may be differing on is what determines the bulk charging current, though I'm not sure.

 

[Stu Jackson]

I'm sure Stu knows all of that, too, what we may be differing on is what determines the bulk charging current, though I'm not sure.

Yes, thanks for your detailed reply, and I do "get it." We are not differing on anything, all three of us know how this stuff works. Bulk charging current is determined by two things: 1) the voltage 2) battery acceptance. Acceptance here is not the term used in the Link 2000 R manual, but is rather the "push back" from the battery's state of charge.

Nice picture of the Link. If you were charging with the alternator, how come the Charge light is on?

I'm going to do an experiment some time soon. I couldn't because I had to reset my Link yesterday. The experiment will be with a 50% SoC on my house bank with my 100A alternator. Might be a week or so before I can get to it.

Although we have finally cleared up the word "acceptance" - thanks , I know that jviss is right in that during rising voltage in bulk the current will be maxed, of course. No disagreement there. Only difference is how long that lasts.

Thank you all for your patience with me.

 

[jviss]

Hi Stu,

The charge light is always on when I'm charging. It goes off when the Accept light comes on. (I'm on a mooring, so no shore power.)

I'm still not clear on your use of the term acceptance. Do you mean this to apply during the absorption phase? Is there a book or other reference where you picked this up?

 

[Maine Sail]

Charged too hard?

Example #1
In this example I have a customer who converted his boat back from AGM batteries to flooded. His alternator & charging system was sized for the previous bank of AGM batteries and included temp compensation for all sources and a 14.7V target voltage.. He charged those Trojan T1275's, at .31C or 31% of the 20 hour rating, and he did this for 9 years! Most flooded battery owners would be happy as a pig in mud to get 9 years. He only got rid of them because he was heading off shore to the Bahama's and did not feel comfortable with the bank being 9 years old..

Example #2
A number of years ago a customer wanted a bigger start/reserve battery for remote cruising in Nova Scotia and Newfoundland. He had a four year old Trojan SCS-150 deep-cycle he was using as a start bank. I could not bear to bring it to the scrap yard, as it was in very good condition. When the cheap start battery in my wife's Honda Pilot started approaching 6 years old I threw in the Trojan SCS-150. 3 years later that battery was still plugging away despite the 130A Denso alternator being sized at 1.3C (10X larger than Trojan's recomendation) and with no temp compensation other than the internal regulators voltage fold back due to heat.

I could go on and on and on with example after example of Trojan flooded batteries being charged faster than Trojan's max 20% and most of those surviving longer than the average boaters banks do. I will stress however that in a deep cycle application charging FDC batteries fast should definitely include temp compensation.

Sadly, in recent years, Trojan has insulated their actual engineers from the field/tech support. While Stacey is pretty good, generally knows her stuff and I believe really applies herself, James, well, I will hold my thoughts on his depth of knowledge. Super nice guy though.

 

[Maine Sail]

Absorption starts when you leave bulk, which is where you reach your voltage set point.

Bingo!

At that transition

This is the transition from CC / constant-current or maximum charger output to CV or constant-voltage.

current should just start to drop from your maximum output.

Again this is absolutely correct. Once the battery becomes voltage limited charge current has nowhere to go but down..

The BatteryUniversity link above seems to say the bulk/absorption transition happens around 70% SOC,

Based on what C rate??

but I'd imagine that depends on the size of your current source (with a larger source transitioning earlier).

Again BINGO!
You can't accurately suggest a Bulk/CC to CV/Absorption transition as a percentage of SoC without also referencing the charge rate. The point at which you attain "absorption voltage" is based on the charge rate.

If you threw a really high current at a flooded lead acid battery it could attain an absorption voltage almost immediately, at 50% SoC. Conversely if we charge it at a very low rate (eg: many PV systems) we won't hit the absorption voltage until a quite high SoC many times well into the upper 90's as a percent SoC...

For example if we charge a high acceptance Lifeline AGM battery at .4C (40% of Ah capacity), starting from 50% SoC, bulk is about 20 minutes and we attain absorption voltage at about 63% SoC. If we charge the same exact battery at .2C (20% of Ah capacity) bulk is about 1:15 minutes and absorption is attained at about 77% SoC. If you charged it at .03C (3% of Ah capacity) from a small PV array the bank won't exit bulk until well into the 90% SoC range.

 

[Maine Sail]

I spoke with a technical support person at Trojan. He first quoted the 13% C(20) limit, and when I told him I had a limited charging time situation, he said I could go to 20%, but no more than 20%.

I see you got the stock "fast charge" answer I had suggested you would a number of posts ago. Course over the years, when you used to be able to talk directly with the actual engineers, I have been told everything from .2C to .25C and even .33C.

 

[jviss]

I can limit the current from the alternator with the Link 2000-R, not the current into the batteries. But I can do it so that while charging the fridge, my biggest single load at 5A, is on constantly, and limit Alt. Amps to 70A, and stay close to or under 30A, depending on other loads.

 

[Stu Jackson]

I'm still not clear on your use of the term acceptance. Do you mean this to apply during the absorption phase? Is there a book or other reference where you picked this up?

I answered this question earlier, you could find it. I just did, reply #11, page 1.
Your Link 2000 R calls the middle stage of charging acceptance.
I am and have been talking about BATTERY acceptance.
Got it now?

 

[jviss]

You may choose to go back to re-read what I've said now with perhaps a better understanding of why I said what I did.

Got it now?

I wrote a rather long reply to this, but I have decided to not bother, since you are compelled to respond to me with condescension. Stu, you are not the only one here who knows anything about battery chemistry and electricity, and not everyone you address is the idiot you apparently think they are.

 

[jviss]

Perhaps there is confusion about the word acceptance. BTW, I seem to recall that the 3 phases of charging (or stages) are bulk, absorption and float, not bulk, acceptance, and float.

You might want to contact Trojan and let them know:

"Trojan recommends using a 3-stage charger. Also called “automatic”, “smart” or “IEI” chargers, which prolong battery life with their programmed charging profile. These chargers usually have three distinct charging stages: bulk, acceptance, and float."

Battery Maintenance

 

[Stu Jackson]

These chargers usually have three distinct charging stages: bulk, acceptance, and float."

You may have to reread this entire thread from the start. I AGREED with you that one of the stages of charging IS acceptance. AND that it appears in literature, your Link 2000 R manual (I've said this twice), and that while some say "bulk, acceptance, float," OTHERS say, "bulk, absorption, float." That's all.
I have been talking about "BATTERY acceptance." Two words, a phrase, if you will. Different thing than a charging phase of acceptance, or absorption.
I have no idea what your reply #35 means.